This invention relates to a photoconductive member for use in a single pass multi-color printing machine, and more particularly, concerns a photoconductive belt having a larger interdocument zone in the photoconductive belt seam area and a smaller sized interdocument zone for all other belt areas. This results in a printing machine that has an asynchronous timing pattern. System software needs to detect the asynchronous interdocument zones and adjust paper copy media handling timing, primarily sheet feed timing, in order to maintain image to copy media synchronization. By implementing an asynchronous timing approach, photoconductive belt length can be optimized and maximum usage of belt length can be used for printing copies thus providing desired print rate and productivity with smaller photoconductive belt length and reduced machine/motor velocities.
In a typical electrophotographic printing machine a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in the irradiated areas to record an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, bringing a developer material into contact therewith develops the latent image. Generally, the electrostatic latent image is developed with dry developer material comprising carrier granules having toner particles adhering triboelectrically thereto. However, a liquid developer material may be used as well. The toner particles are attracted to the latent image, forming a visible powder image on the photoconductive surface. After the electrostatic latent image is developed with the toner particles, the toner powder image is transferred to copy media. Thereafter, the toner image is heated to permanently fuse it to the copy media.
It is highly desirable to use a photoconductive member of this type in an electrophotographic printing machine to produce color prints. In order to produce a color print, the printing machine includes a plurality of stations. Each station has a charging device for charging the photoconductive surface, an exposing device for selectively illuminating the charged portions of the photoconductive surface to record an electrostatic latent image thereon, and a developer unit for developing the electrostatic latent image with toner particles. Each developer unit deposits different color toner particles on the respective electrostatic latent image. The images are developed, at least partially in superimposed registration with one another, to form a multi-color toner powder image. The resultant multi-color powder image is subsequently transferred to a sheet. The transferred multi-color image is then permanently fused to the sheet forming the color print.
Electrophotographic printing machines to date use a photoconductive member that is a seamed belt coated with a photoconductive material. Images are laid down on the belt such that an interdocument zone follows the image area, and since the seamed area of the belt results in an image quality defect, the seam area of the belt is kept within an interdocument area. Thus, the interdocument zones are limited to receiving latent process control patches that enable the electrophotographic process to be monitored and controlled.
In the past the photoconductive belt length was determined by a combination of various parameters. These parameters consist of time constants required between each of the steps in the electrophotographic process such as the physical size of the electrophotographic components, size of the patches required for electrophotographic process controls, and image panel sizes. Thus, in a given electrophotographic printing machine having a given architecture, with N image panels there are N interdocument zones including the one placed over the seam. In previous machines for a given pitch mode, the interdocument zones were all of equal size, and the system timing was constant and synchronous.
A multicolor printing machine of this type having architectures using a single sized interdocument zone requires an overly long photoconductive belt and a large frame structure to support it. A large machine height results when the major axis of the photoconductive member is aligned vertically and serious concerns over machine operability, service, shipping, and machine handling arise. Likewise, a photoconductive belt having an overly long length has very low yields when made in large quantities. In order to reduce of the machine height and photoconductive belt length an asynchronous timing approach was developed wherein firstly, an inter seam zone, on the photoconductive belt, includes the physical belt seam as well as image-on-image registration patches. Secondly, while using the inter seam zone for monitoring image-on-image registration, interdocument zones include patches that govern process control. Finally, the machine timing of the system is adjusted so that copy media is synchronized with the asynchronous placement of the images on the photoconductive belt. This requires system software to adjust system timing to synchronize media with images.
Various types of multi-color printing machines have heretofore been employed. The following disclosure appears to be relevant:
U.S. Pat. No. 5,946,533
Patentee: Omelchenko et al.
Issued: Aug. 31, 1991
U.S. Pat. No. 5,946,533 discloses a single pass, multi-color electrophotographic printing machine architecture which uses a vertically oriented photoconductive belt. Transfer of toner powder images occur at the lowermost portion of the photoconductive belt. The photoconductive belt is elliptically shaped, having a major and minor axis. N image recording stations are positioned adjacent an exterior surface of the photoconductive belt on one side of the major axis thereof. Nxe2x88x921 image recording stations are positioned adjacent the exterior surface of the photoconductive belt on the other side of the major axis thereof. The image recording stations record electrostatic latent images on the photoconductive belt. This architecture optimizes image registration while minimizing the overall height of the printing machine.
In accordance with the features of the present invention, there is provided a photoconductive member for use in a single pass multi-color printing machine. The photoconductive member is composed of an inter seam zone having a physical seam. The inter seam zone includes one of a plurality of image-on-image registration marks respective to a particular color latent image formed on the photoconductive member in a single pass. A plurality of interdocument zones is also included on the photoconductive member wherein process control marks are formed. While the inter seam zone is used for monitoring image-to-image registration, the process control marks are monitored to adjust the timing of the printing machine so that copy media synchronizes with an asynchronous placement of the images on the photoconductive member.